1. Field of the Invention
This invention relates to a radiation measuring apparatus, particularly, one suitable to be utilized in a dose rate meter.
2. Prior Art
FIG. 1 is a block diagram showing a radiation measuring apparatus as a conventional dose rate meter. In FIG. 1, reference numeral 1 is a radiation detector for outputting a pulse signal whose pulse height corresponds to radiation energy detected by the radiation detector 1 such as a scintillation counter or a semiconductor radiation counter; 2, a pulse amplifier which amplifies the pulse signal output from the radiation detector 1; 3, a pulse height discriminator which compares the pulse height of the pulse signal amplified by the pulse amplifier 2 with a predetermined discrimination voltage; 4, a pulse count rate meter which is supplied with a pulse signal discriminated by the pulse height discriminator 3; and 5, an indicator which indicates an output voltage of the pulse count rate meter 4.
Next, the operation will be described. The radiation detector 1 detects radiation and generates a pulse signal, and the pulse amplifier 2 amplifies the pulse signal. The pulse height discriminator 3 responds to pulses among the pulse signal whose pulse height is larger than a predetermined discrimination voltage preset thereto upon receiving the pulse signal from the pulse amplifier 2 and generates output pulses. The pulse count rate meter 4 generates an output voltage (or current) signal proportional to the counting rate (frequency) of the output pulses from the pulse height discriminator 3. The indicator 5 indicates the output voltage (or current) signal from the pulse count rate meter 4. Since the counting rate of the pulse signal is proportional to a dose rate of the radiation incident on the radiation detector 1, the dose rate can be measured by calibrating readings of the indicator 5 with respect to dose rates. Incidentally, the pulse height discriminator 3 is employed for discriminating a pulse signal due to the radiation from other noise pulses. Also, the radiation which the radiation measuring apparatus as a dose rate meter regards as a measuring object is X- or gamma-radiation.
Since a conventional radiation measuring apparatus is constituted as described above, there is a problem that sensitivity to dose rate is different, depending on radiation energy. In particular, in the case where the radiation detector 1 is a scintillation counter or a semiconductor radiation counter, the sensitivity becomes higher at a range of lower radiation energy as shown by a sensitivity characteristic curve against radiation energy in FIG. 2. As a countermeasure for this, there is adopted a method in which the radiation detector 1 is covered with a radiation absorbing filter so as to reduce the sensitivity at the range of lower radiation energy. But, this method poses another problem that the lower limit of the span of measurable radiation energy is narrowed.